I should also mention that my wife is also shooting in this match (on the same squad), and a couples theme might go well.

See if you can find a black pinstripe suit (Goodwill, Salvation Army) that you don't mind getting dirty. Find a tight fitting black bodysuit for the wife and go as John Steed and Emma Peel from the "Avengers".
My wife's Idea, she's English.

Edit: You could use the same suit and have your wife go a "Gun Moll" from the prohibition era.